The notes of the open srings of a guitar in standard tuning are (starting with the thickest string) E, A, D, G, B and E. To remember this, Elephants And Donkeys Grow Big Ears.
The easiest way to tune your guitar is with an electronic tuner. They come in various types, but are really cheap these days, and well worth the investment. There are also internet tuners, mobile phone and ipod tuners these days. I use the Polytune app for iPhone/iPod.
It is also vital to be able to tune by hear. so this is how it's done. Assuming the 6th string is in or at least nearly in tune, hold down the the note on the 5th fret. The note produced should be the same as the open 5th string. If it is not, turn the tuning peg on the 5th string until the notes produced are the same. Once this is completed hold down the 5th fret on the 5th string. This should produce the same note as the open 4th string. Again if this is not the case, then turn the tuning peg on the 4th string until it is the same. Hold down the 5th fret of the 4th string. This note should be the same as the open 3rd string. Again if it is not, turn the tuning peg until it is the
same. This time hold down the 4th fret of the 3rd string. This fret should produce the same note as the 2nd string. If does not, then turn the tuning peg of the 2nd string until it does. Finally, hold down the 5th fret of the 2nd string, this should produce the same note as the open 1st string. If it is not,
turn the 1st tuning peg until it is the same.
This should have put the guitar in tune. It is not very easy to do and does take practice.